This invention relates to a high frequency electrosurgical instrument used in an endoscope, which is provided at its distal end portion with an electrode wire supplied with a high frequency current and which is inserted into a coeliac cavity through an endoscope in order to cut an affected part.
A known electrosurgical instrument of this type is constructed as shown in FIG. 1. The instrument comprises a flexible tube 1 made of a synthetic resin such as fluorine resin. The tube 1 has at its distal end portion a pair of electrode wire holes 2 which are set apart in the axial direction of the tube 1. An electrode wire 3 extends through the tube 1, comes out of the tube 1 through one of the holes 2 which is remote from the distal end of the tube 1, enters the tube 1 through the other hole 2, and turns back to extend through the tube 1 to the proximal end of the tube 1 to have its end secured to the proximal end portion of the tube 1.
The tube 1 is guided through an endoscope inserted in a coeliac cavity until its distal end portion is placed near the coeliac cavity. Then, an operation section provided at the proximal end of the tube 1 is operated so as to pull the electrode wire 3. As the wire 3 is pulled, the distal end portion of the tube 1 is bent to form a bow with the wire 3 extended as a string, as illustrated in FIG. 2. That portion of the wire 3 which makes the string of the bow is brought into contact with an affected part in the coeliac cavity. A high frequency current is applied between the electrode wire 3 and the patient so that the affected part is cut.
The known electrosurgical instrument is disadvantageous in some respects. First, the wire 3 is likely to cut the tube 1 by the tension of the wire 3 and the heat produced during the high frequency electric current, thus forming a slit extending from the hole 2 in the axial direction of the tube 1. If this happens, that portion of the wire 3 which makes the string of the bow is moved downward, as shown in FIG. 3, from the position indicated by chain lines to the position indicated by solid lines. Secondly, if the wire 3 is pulled too much, the distal end portion of the tube 1 is collapsed at the middle point as shown in FIG. 4.